The invention relates to a method for non-destructive determining of material properties of electrically conductive components using electromagnetic eddy current testing.
Light metals are increasingly used in vehicle construction in order to save weight. The structural components used in this context are frequently made as cast aluminum parts. It is desirable to be able to assess these simply and quickly with regard to their ductility/deformation properties. Hitherto, this involved the use of crash tests, bend angle tests, ductility testing by means of punch rivet tests and drop tower tests for test samples. All of these test methods have substantial drawbacks. For example, the crash test is a destructive, extremely cost-intensive and time-intensive testing method, often with difficult evidence and conclusions. Bending angle measurement is also destructive and permits no real testing of the material properties.
Eddy current testing is known as a non-destructive testing method for determining mechanical material properties of electrically conductive materials. It uses the effect that most impurities and defects in an electrically conductive material also have an electrical conductivity or a permeability that is different to that of the actual material.
Thus, the eddy current principle in the context of non-destructive determining of mechanical material properties is described for example on pages 19-21 of Mork's dissertation “Qualitäatsbewertung und -regelung für die Fertigung von Karosserieteilen in Presswerken auf Basis neuronaler Netze [Quality evaluation and control for the production of bodywork parts in pressing plants on the basis of neural networks]” dated May 30, 2011 and published by Herbert Utz Verlag of Munich in Forschungsberichte IWB [IWB Research Papers], Band [Volume] 251. These properties include tensile strength, yield strength, extension and others. Electrically conductive materials can be measured contactlessly and in a very short time by applying a temporally changing magnetic field. Both mechanical and electrical properties depend on the material state and therefore on the structure, the alloying constituents, the grain size, the dislocation density, the anisotropy and so forth. There is therefore a relationship of correlation between electromagnetic and mechanical properties of a material. This dissertation describes the eddy current testing method for determining mechanical, that is to say static, material properties, in the pressing plant during production of bodywork parts, in order to identify production errors in a timely fashion and as fully automatically as possible.
The present invention has the object of replacing the known destructive testing methods in the context of cast structural components.
It has surprisingly been found that eddy current testing can safely and reliably identify, in addition to the known static material properties, also the impact-dynamic deformation behavior of cast samples, in particular their behavior in the event of a crash, if use is made of a high-resolution eddy current sensor that is adapted to the cast-specific conductivity. Thus, a cost-effective, rapid and reproducible measurement method with objective crash evaluation criteria for cast parts is available. The term sample in the context of this invention is to be understood not only to mean cast samples but also finished cast components, in particular structural components for vehicle construction.
In order to quickly obtain, objective and reliable conclusions regarding the crash behavior of the samples, the performance of the samples may be compared to a reference sample.
The comparability of the measurement results may be enhanced by measuring the samples at the same testing temperature.
Particularly advantageously, the method according to the invention can be used in the context of structural components such as longerons in motor vehicles, which are made of an AlSiMg alloy.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.